This invention relates to apparatus which is operable to provide a working thrust at a remote station by displacement of liquid under pressure from a master cylinder to a slave cylinder at the remote station; the apparatus comprising the master cylinder; the slave cylinder; a conduit which connects a liquid pressure outlet of the master cylinder to an inlet of the slave cylinder; and a liquid reservoir which has a port which communicates with the liquid containing chamber thereof below the normal level of liquid contained therein and which is in communication with a port in the master cylinder which is open when the master cylinder piston is at the end of its stroke remote from the master cylinder outlet so that the liquid containing chamber of the reservoir is in communication with the bore of the master cylinder between the master cylinder piston and the liquid pressure outlet and which is closed when liquid is displaced under pressure from the master cylinder through the liquid pressure outlet by movement of the master cylinder piston towards the liquid pressure outlet, and a vent port which communicates with the liquid containing chamber of the reservoir above the normal level of liquid contained therein and which places the space within the liquid contained chamber that is above the normal level of liquid therein in communication with an air space which is at a pressure which is substantially atmospheric. Such apparatus will be identified in this specification as apparatus of the kind referred to from hereon. The invention is concerned particularly with apparatus of the kind referred to that is designed for use to provide the thrust required to release a motor vehicle friction clutch.
It is common practice for the various components of friction clutch release apparatus of the kind referred to to be installed separately on the vehicle and for the connections between those components to be made only after those components have been installed. It is then necessary to fill the apparatus with liquid and to bleed the apparatus in order to remove entrapped gas from the liquid filled parts of the system.